A unidirectional microphone generally has a directional axis aligned with its central axis.
Patent literature 1 describes a structure in which two unidirectional microphones of this type are used to effectively obtain stereo sounds. In the structure in patent literature 1, for example, two sound holes (primary sound hole and secondary sound hole) offset relative to the central axis of the microphone is disposed in a holder for holding the microphone so that the directional axis is offset relative to the central axis of the microphone. In the structure, the primary sound hole and the secondary sound hole are placed on mutually opposite sides of the central axis of the microphone so that the directional axis is tiled from the central axis of the microphones to increase the angle formed by the directional axes of the two microphones.